1. Field of the Invention
This invention relates to a process for making high molecular weight, cross-linked lignin gel beads. More particularly, this invention relates to an improved process for making lignin gels in bead form by reacting an emulsion containing an aqueous solution containing a water-insoluble lignin with a cross-linking agent in the presence of alkali. The invention also relates to a process for the separation of compounds by contacting a solution of the compounds with the lignin gel beads.
2. The Prior Art
Colloid gels from waste sulfite liquor are described in U.S. Pat. No. 1,839,061 to R. G. Tellier. These gels are used as a medium for treating an argillaceous material to form a colloid gel which contains organic matter and a mordant. In U.S. Pat. No. 2,874,545, R. H. Twining describes a process for forming a water-insoluble gel by reacting lignosulfonates with solutions of boric acid and a soluble chromate. In U.S. Pat. No. 3,759,826, V. F. Felicetta and E. G. King describe processes for making lignin gels by polymerization under acid conditions or cross-linking with formaldehyde. These gels are useful for the fractionation and recovery of water-soluble compounds by gel permeation.
In the past lignin has been reacted with epichlorohydrin. For example, in U.S. Pat. No. 3,672,817 to S. I. Falkehag, a water-soluble sulfonated lignin was reacted with epichlorohydrin to block phenolic hydroxyl groups of the lignin to reduce fiber staining and diazo dye reduction of these lignin dispersants. In U.S. Pat. No. 4,001,202, P. Dilling and G. Prazak disclose a process for producing a water-soluble dispersant by reacting a sulfonated lignin with epichlorohydrin to both block a portion of the free-phenolic hydroxyl of the lignin and to cross-link lignin molecules. On the other hand, the lignin gel beads made according to the process of this invention are not water-soluble.
It is, therefore, the general object of this invention to provide a process for producing lignin gels in bead form.
Another object of this invention is to provide a reversibly swellable lignin gel in a form not requiring any disintegration of the reaction product form for use in gel permeation.
Yet another object of this invention is to provide a process for the fractionation and recovery of compounds by gel permeation or selective sorption depending on molecular dimensions or polar character using lignin gel beads.
Other objects, features and advantages of this invention will be evident from the following detailed description of the invention.